This invention relates to a vehicle-running control device which changes speed and transmits engine power by a torque converter.
In a vehicle where speed is changed and engine power is transmitted by a torque converter, when a shift lever is in a forward position or reverse position, a creep phenomenon occurs wherein the vehicle moves at a very low speed even if the accelerator pedal is not depressed. This phenomenon occurs because the torque converter transfers power according to the output of the idle rotation of the engine. In an industrial vehicle, especially a fork lift truck provided with a torque converter, when the vehicle is running very slowly for picking up or discharging a load, workability is improved by making use of this creep phenomenon. However, when an operator familiar with industrial vehicles without a torque converter operates a vehicle with a torque converter, the vehicle may move unintended by the operator.
Tokkai-Hei 11-166617 published by the Japanese Patent Office in 1999 discloses a vehicle-running control device for eliminating the disadvantages due to creep. For example, in the state where the accelerator pedal is not depressed even if the shift lever is in the forward position (or reverse position), this vehicle-running control device prevents supply of oil pressure for engaging the forward clutch (or reverse clutch), and thereby prevents the vehicle from creeping.
However, if the creep phenomenon specific to a vehicle with a torque converter is merely suppressed, the easy operability inherent in such a vehicle is impaired. In particular, the operability of an operator who attempts to use creep effectively is impaired. Thus, it is difficult for the vehicle-running control device of the prior art to satisfy all operators.
It is therefore an object of this invention to provide a vehicle-running control device which can control the creep of a vehicle equipped with a torque converter.
In order to achieve above object, this invention provides a vehicle-running control device having a torque converter connected to an engine, and a forward clutch and reverse clutch for transmitting the torque from the torque converter to an output shaft.
The vehicle-running control device comprises a hydraulic circuit for operating one of the forward clutch and reverse clutch, the hydraulic circuit having a change-over valve which can be prevented from supplying the pressurized fluid to both the forward clutch and reverse clutch, and a pressure control valve which adjusts the pressure of the pressurized fluid supplied to the operating clutch; a first sensor for detecting that the change-over valve supplies the pressurized fluid to the forward clutch or the reverse clutch; a second sensor for detecting that the accelerator pedal is released; a sensor for detecting a vehicle speed; and a controller.
The controller functions to compare a predetermined target speed range with the vehicle speed, when the change-over valve supplies the pressurized fluid to one of the forward clutch and reverse clutch and the accelerator pedal is not depressed, and to command the pressure control valve to control the torque transmitted by the operating clutch according to the comparison result so that the vehicle speed is within the predetermined target speed range.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.